Chemical process of producing an iron-copper alloy powder

ABSTRACT

A PARTICULATE ALLOY OF IRON INTIMATELY INFILTRATED WITH FROM ABOUT 1 TO ABOUT 50% BY WEIGHT OF COPPER IS PRODUCED BY MIXING A REDUCIBLE COMPOUND OF IRON WITH AN APPROPRIATE PROPORTION OF COPPER COMPOUND SELECTED FROM THE GROUP CONSISTING OF ELEMENTAL COPPER AND REDUCIBLE COMPOUNDS OF COPPER, THE MIXTURE BEING HEATED UNDER REDUCING CONDITIONS AT A TEMPERATURE BETWEEN ABOUT 1010 AND 1150*C. UNTIL THE REDUCIBLE COMPOUNDS ARE SUBSTANTIALLY COMPLETELY REDUCED TO THE METAL STATE.

A. ADLER 3,583,864

CHEMICAL PROCESS OF PRODUCING AN IRON-COPPER ALLOY POWDER June 8, 1971 2Sheets-Sheet I.

Filed May 5. 1969 FIG .l MICRON F l G FIG.3

0. l MICRON f WM l0 O MICRONS 10 0 MICRONS ATTORA E) June 8, 1971 A.ADLER CHEMICAL PROCESS OF PRODUCING AN IRON-COPPER ALLOY POWDER FiledMay 5, 1969 2 Sheets-Sheet l FIG;5

l. 0 MICRON ATTOPA/F) United States Patent Oflice Patented June 8, 1971US. Cl. 75--.5BA 21 Claims ABSTRACT OF THE DISCLOSURE A particulatealloy of iron intimately infiltrated with from about 1 to about 50% byweight of copper is produced by mixing a reducible compound of iron withan appropriate proportion of copper compound selected from the groupconsisting of elemental copper and reducible compounds of copper, themixture being heated under re ducing conditions at a temperature betweenabout 1010 and 1150 C. until the reducible compounds are substantiallycompletely reduced to the metal state.

CROSS REFERENCE TO RELATED APPLICATIONS This application is acontinuation-in-part of application Ser. No. 471,767 filed July 13,1965, now Patent No. 3,489,548.

BACKGROUND OF THE INVENTION This invention is concerned with alloys ofcopper and iron, and more particularly with novel iron powderspreinfiltrated with copper, and with processes for their preparation.

As employed herein and in the appended claims, an alloy is defined to bea substance having metallic properties and composed of two or morechemical elements of which at least one is elemental metal. It has inthe past been recognized that the physical properties of iron areimproved by alloying with copper. Since these metals are virtuallyinsoluble in each other at room temperature, and since their mutualsolubility is quite limited even at elevated temperatures, variousexpedients have been employed in an attempt to bring them into intimateassociation. Thus, copper and iron powders have been blended and moldedinto finished objects by the techniques of powder metallurgy. Inaddition, the infiltration process has been employed, i.e. filling thepores of a sintered powder metallurgy part, of iron or steel in thiscase, with a metal or alloy of lower melting point, e.g. copper.

These prior methods for the preparation of copper-iron alloys arecharacterized by important problems and disadvantages. Blended copperand iron powders are subject to segregation in storage and shipment.More important, even very finely divided, blended powders do not providethe degree of homogeneity which affords optimum properties. In addition,sintering of compacted copper-iron powder blends results in expansion ofthe compact, representing a porosity increase which is a major factor ininferior strength, molding flaws and high rejection rate.

A relatively simple procedure has now been discovered for thepreparation of novel copper-iron alloys in powder form, offeringsubstantial cost advantages over conventional infiltration techniques.This procedure imparts to the new powders a unique microstructure,characterized by a more intimate admixture of the elements, to which thesuperior physical properties which result may be attributable. Uponsimple pressing and sintering, the new particulate alloys shrink tohigh-density products of great strength.

SUMMARY OF THE INVENTION In essence, the process of the presentinvention entails blending a reducible iron compound with copper or witha reducible copper compound, and reducing these reactants to themetallic state at elevated temperature. The relative proportions areselected to yield a product containing from about 1 to about 50% byweight of copper.

DESCRIPTION OF THE FIGURES The distinctive metallographic features ofthe new alloys will be better understood by reference to theaccomf'panying illustrations, which are photographic reproductions ofhighly magnified electron microscope photomicrographs. Each photographdepicts a portion of a single particle of one of the new alloys,asetched in a 3% solution of nitric acid in alcohol in order to erodethe copperrich areas.

FIG. 1 illustrates an alloy of iron with 7% by weight of copper,prepared by the process of the present invention and enlargedapproximately 100,000 diameters.

FIG. 2 shows the alloy of FIG. 1 after heat treatment as detailedhereinafter, also enlarged approximately 100,- 000 diameters FIG. 3depicts an alloy of iron with 20% by weight of copper, prepared inaccordance with the present invention and enlarged approximately 3600diameters.

FIG. 4 shows the alloy of FIG. 3 after heat treatment, also enlargedapproximately 3600 diameters.

FIG. 5 shows a portion of the particle depicted in FIG. 4, this timeenlarged approximately 17,700 diameters.

The salient features of these illustrations will be referred tohereinafter, in connection with a discussion of the microstructure ofthe new products.

DETAILED DESCRIPTION OF THE INVENTION Copper sinters at about 825850 C.,and it melts at about 1083 C. in the pure state and at about 1095 C.when it contains 3.2% or more of iron In order to achieve the uniquelyintimate consolidation of the iron and copper which characterizes theinvention, it is essential that the temperature during the reductionstep reach at least C. above the sintering temperature of copper. Inaddition, it has been found that inferior results are achieved atreduction temperatures below about 1850 F. (l0l0 C.). Such reductionconditions produce a powder alloy of low apparent density containingexcessive fines and characterized by poor flow and frequently by highshrinkage upon pressing and sintering. Further, and particularly inreduction with carbon (e.g. coke), temperatures below 1850 F. requireexcessive time for adequate reduction or lead to substantiallyincomplete reduction. The minimum practical and economic reductiontemperature is 1850 F.

However, particularly for those alloys containing in excess of 20% byweight of copper, reduction temperatures at or above the copper meltingtemperature tend to cause agglomeration of the reduced product to a masswhich can be broken down into smaller particles only with difficulty.Accordingly, especially when alloys of such high copper content areprepared, it is best to keep the reduction temperature below the meltingpoint of copper. In all cases, however, reduction temperatures aboveabout 1150 C. are undesirable, since they favor extensive productagglomeration, producing a tough, hard mass which is impossible to grindto metal powder by any economic means. Best results have been achievedat 18502000 F. (10l01093 C.) and especially at 1900- 1950 F. (10381066C.).

Under the described conditions, the reactant mixture is reduced to aparticulate alloy of iron intimately infiltrated with copper, withoutthe need for the copper to flow through the mass of iron to saturate thepores as is the case in conventional infiltration of molded ironcompacts. During the new process, the oxide or other reducible ironcompound undergoes a solid state reduction. Where the reduction isconducted below 1094 C., but at least 100 above the copper sinteringtemperature, the copper does not liquify, but the reduced solids undergograin boundary diffusion, with comparable results. These lower reductiontemperatures are especially preferred in the production of alloys ofhigh copper content, as previously discussed, and the high copper volumefractions are believed to favor products of infiltrated nature.

When reference is made in this disclosure and in the appended claims toparticulate alloys of iron infiltrated with copper, this expression isintended to describe individual particles containing both copper andiron in intimate mutual dispersion, as distinguished from mere blends ofcopper powder with iron powder, and as further distinguished fromparticles of the one element merely coated with the other.

By their nature, the new particulate alloys of the present invention arenot subject to segregation into the individual elements in storage orshipment. They may be truly termed preinfiltrated alloys, since they aredirectly moldable by conventional powder metallurgy techniques to usefulparts, without the need for a separate penetration of liquid copper intoa molded iron part as practiced in conventional infiltration.

Any reducible iron compound may be employed in the new process,including iron salts or any oxide of iron such as hematite, magnetite,beneficiated magnetite ores, flue dusts, synthetic oxides or reduciblemill scales, e.g. from rolling mill operations. By reducible mill scalesis meant those which are reducible to the extent of about 99% or better,such as carbon steel mill scale and low alloy steel mill scales.

The source of copper may be elemental copper, such as reduced copperpowder, atomized copper, electrolytic copper powder orhydrometallurgical copper powder. However, it will usually be lessexpensive to employ an oxide of copper, either precipitated ormechanically produced, such as cuprous oxide, cupric oxide, copper millscale, copper flue dust, or cement copper, a by-product of mine wastewater which typically contains about 50- 98% cuprous oxide. Where copperoxides are employed, it is sometimes beneficial to incorporate nitricacid in the reaction charge, to promote a more intimate dispersion.Alternatively, cupric nitrate or other water-soluble copper salt, may beemployed in water solution as the copper source.

In addition to copper and iron, nickel, cobalt, molybdenum or tungstenmay be included, or reducible compounds of these elements, such asnickelous acetate, cobaltic oxide, molybdic oxide, or tungsticanhydride. Such elements will generally be employed in minor proportion,i.e. up to about 6% by weight of any one element or a total of up toabout 12% by weight in the case of several in combination, in order toimprove strength. Such elements may be added in the form of solublesalts such as nitrates or acetates, for optimum dispersion, or ascompounds in combination with an acid or base solvent, such as ammoniawater or nitric acid.

Those reactants are preferred which have particle sizes finer than 250microns, and especially preferred are iron compounds finer than about 50microns and copper compounds finer than about 20 microns, since thesefavor the most intimate interdispersion of the elements.

While not essential, it is often advantageous to blend the reactantswith an aqueous dispersion of an organic adhesive, to minimize dustinglosses or segregation of the reactants during handling and subsequentprocessing.

Suitable binders include animal protein glue, methyl cellulose,hydroxyethyl cellulose, carboxymethyl cellulose, sugar and the like.Such compounds are readily decomposed at the reduction temperature andshould preferably be low in ash content. Adhesive levels of about 0.5%of the total batch weight are usually entirely adequate, the proportionof water usually being up to about 18% of the total batch.

Where an adhesive is employed, the blending of reactants may beadvantageously conducted in a mix muller or chaser, which will form theingredients into hard pellets up to about an inch in diameter withlittle or no secondary grinding. These pellets may be charged to thereduction furnace without drying. If no adhesive is employed, thereactants are thoroughly blended before charging to the furnace.

Reducing conditions may be provided within the furnace in the form of agaseous reducing atmosphere, e.g. hydrogen or carbon monoxide, orsources of such agents including dissociated ammonia, water gas,producer gas and the like. Alternatively, the reducing conditions may beprovided by incorporating finely divided carbon within the reactantmixture, and this procedure is preferred for economic reasons. Suitableforms of carbon include lamp black, petroleum coke, anthracite fines,carbon black, bone black or graphite. The minimum carbon levels, beingdependent on the particular reactants and reactant proportions, may beestimated from the stoichiometry of the reaction, but optimum levels arebest determined by experiment. Carbon levels of about 8-12% are typical.Even where a gaseous reducing atmosphere is provided, it is sometimesbeneficial to incorporate a minor proportion of carbon, particularly inlarge batches, to ensure effective reduction. As is well known in thereduction art, where carbon is the principal reducing agent it isordinarily desirable to sweep the furnace with a carrier gas, to driveoff the volatile reduction products and prevent re-oxidation. Suitablecarrier gases include endothermic gases high in nitrogen, exothermicgases, methane, propane, natural gas, or the like. Manufactured gas,producer gas or hydrogen may, of course, also be used if desired.

The reduction is continued until the reducible compounds aresubstantially completely reduced, i.e. about 93-98% reduced. Duringreduction, the product particles usually form a lightly sintered sponge,which may readily be subdivided to final particle size specifications bymilling. It has been found that a residual oxygen content of 2% or moreyields a particularly friable sponge which is broken up more easily thansponges of lower oxygen content. The time required to carry thereduction to this level will vary with the reducing conditions, thebatch size, and the particular reactants selected. Ordinarily, reductionis substantially complete on a laboratory-size batch in from about 30minutes to two hours. It is undesirable to prolong the reductionunnecessarily, e.g. to the point of quantitative oxygen removal, sincethis may lead to difiiculty in breaking up the sponge.

After cooling, the product may be ground in a hammer mill or pulverizerto final particle size specifications, generally to pass 60 or mesh.

The resulting powders may be molded into useful shapes by conventionalpowder metallurgy techniques, i.e. by compacting at about 10-60 tons persquare inch and then sintering under non-oxidizing conditions atelevated temperature, preferably at or above the melting point of copperfor optimum properties. It should be noted that where blended copper andiron powders are molded in this fashtion, it is necessary at high coppercontent to sinter below the melting point of copper, with attendantstrength disadvantages, in order to avoid loss of copper by blistering.This is caused by agglomeration of the copper-rich masses in such blendsduring sintering. It is also important to note that the sintering ofpremixed copper and iron powders results in an expansion of the compactas a reflection of the alloying process. In the new particulate alloys,on the other hand, any expansion as a result of alloying occurs duringthe reduction step and not during the sintering of the compactedparticles. The sintering of these new alloys represents a consolidationof the pre-infiltrated or alloyed particles. This results in shrinkageof the sintered compact, which, as previously noted, is more desirable.

Sintered parts prepared from the particulate alloys of the describedreduction process possess good physical properties even without furthertreatment. The degree of shrinkage and the resulting strength dependmainly on the copper content, with maximum shrinkage and maxi mumstrength at about 30% copper.

A further important feature of the present invention resides in thediscovery of a novel heat-treatment process for the alloy powders, whichleads to a striking and unprecedented increase in the density andphysical strength of the final sintered compact. This heat treatmentrepresents in effect a densification or preshrinkage, reducing thedegree of shrinkage in the final sintering step without, however,leading to the undesirable expansion effect referred to previously.

The ot'y transition temperature of iron lies at about 910 C., but in thecase of iron containing over 3.5% copper this transition occurs at about835-850 C. It has been found that heat treatment of the new alloypowders is most effective at a temperature between the a-q transitiontemperature of the iron-rich phase and a temperature about 150 C. lower.The best results are obtained by heat treating at a temperature lessthan 50 C. below the a-q transition, preferably at about 825-845 C. Suchconditions lead to development of the highest density, strength andhardness, with minimum shrinkage, upon sintering. Properties begin todrop abruptly from the optimum when the heat-treatment temperatureexceeds 845-850 C.

For best results, the powder should be heat treated for at least aboutminutes before cooling. This should afford sufficient time for the majorportion of the excess copper within the supersaturated iron to separateas a fine precipitate. The maximum time is not critical, and periods upto hours may be used. However, there is no advantage to heat treatingfor more than 4 hours. Of course, some time may be needed to heat thebatch to the operating temperature, and this will vary with the size ofthe batch.

If the reduced powder subjected to heat treatment contains over 2%oxygen, it is best to heat treat under reducing conditions, so as tofurther reduce oxygen content below 2% and preferably below 1% duringthis step. If, however, the oxygen content is already 2% or less, aninert atmosphere may be employed if desired.

The powders are discharged from the furnace as loosely sintered masses,which may be re-ground to particles finer than 60-80 mesh in the samemanner as after the primary reduction process.

Heat treatment as described greatly enhances the properties of the alloypowders of this invention. After compacting and sintering, the productsexhibit outstanding tensile strength, as may be seen from the appendedexamples. It should be noted that those alloys containing about 16%copper have tensile strengths above 45,000 p.s.i.; while 610% copperyields 60,000 p.s.i. or more; l040% copper yields 75,000 p.s.i. or more;and 40-50% copper yields, tensile strength above 65,000 p.s.i. By way ofcomparison, sintered parts made from preblended powders have tensilestrengths which level off at 4045,000 p.s.i., and this is substantiallyunaffected by prior heat treatment of the powder blends.

In addition, sintering shrinkage is greatly reduced as a result of heattreatment of the new alloys, density is substantially increased, andporosity reduced. Each of these advantages is illustrated quantitativelyin the examples.

Such sintered properties are within the range of or superior to those ofthe convention infiltrated part, yet they are obtained by the rathersimple and cheap pressing and sintering process rather than by the moreinvolved and costly infiltrating technique.

A preliminary insight into the microstructures of the new alloys isprovided by their X-ray diffraction patterns. An alloy containing 20%copper displays essentially the same pattern after primary reduction andafter heat treatment: both an a-iIOIl-IiCh phase and an e-copperrichphase is detected. The diffraction pattern of a 7% copper alloy afterheat treatment is substantially similar, except for the expectedindication that a lower proportion of the copper-rich phase is present.However, the 7% alloy after primary reduction exhibits a patterncorresponding to a single a-iron-rich phase. In each of these diagrams,the iron peaks are relatively flattened, the copper peaks sharper.

The failure to resolve a second phase by X-ray diffraction in the 7%copper alloy after reduction is rather surprising, indicating thatalloys of copper content below the solubility limit in iron at thereduction temperature (about 8% at 1125 C.) retain the copper insolution after primary reduction. This may be related to the rate ofcooling upon removal from the furnace, the temperature dropping to about490 C. in the first minute in the typical case, thereby quicklytraversing the range of maximum solubility change. (The solubility ofcopper in iron at 500 C.

is only about 0.25% On the other hand, X-ray data show that subsequentheat treatment within the specified temperature range for 5 rrrinutes ormore does result in precipitation of an X-ray resolvable copper-richphase.

A more accurate insight into the microstructures is gained bymicroscopic examination of the alloy particles, mounted, polished, andetched with nitric acid to erode copper-rich areas and thereby delineatethe phases.

In those alloys containing from about 1 to 10% copper the microstructureis seen to be highly uniform, with the copper content up to about 8%dispersed within the iron grains in the form of particles less thanabout 1000 A.

(0.1g) in diameter. At 250 power magnification, no clearcut grainboundaries can be seen, and it is necessary to turn to the highermagnification of the electron microscope for further delineation. InFIG. 1 is shown a 7% copper alloy of iron after primary reduction, andFIG. 2 shows the same alloy after heat treatment, both views enlargedabout 100,000 diameters. The depressions represent areas where copperwas removed by the etching acid, and the fineness of the dispersion isreadily apparent. When the fields are surveyed further, it is found thatthe specimen after reduction displays dispersed copper-rich particlesabout 350 A. in diameter arranged in clustered bands, with an averagedistance of about A. between copper particles. The clusters areseparated from each other by distances ranging from as little as 500 A.to as great as about 0.75 micron. Between the clusters, copperrichparticles also averaging about 350A. in diameter are detected, but it islikely that particles smaller than the 50 A. resolution limit are alsopresent. It is likewise possible to detect cracks in the microstructure,about 0.1-0.3 in length by 400-900 A. in width, as well as angular voids0.1-0.9,u. in diameter. Upon heat treatment, the cracks are no longervisible, and the clusters now appear in bands or rings about l0ni5 inlength by 3,1.LIL1 in width. The copper particles in these rings arfound to average about 400 A. in diameter, with an interparticle spacingof about 150 A. Those copper particles between clusters which areresolved average about A. in diameter, with an interparticle spacing ofabout 550 A.

Microscopic examination of those alloys of the present invention whichcontain in excess of 10 and up to about 50% by weight of copper revealsthat they contain unusually fine and closely packed iron-rich grains,less than about 35 in their major or largest diameter, with an averageseparation between adjacent iron grain boundaries of 7 less than about5,14, in a primary copper-rich matrix. These iron-rich grains contain ahighly uniform dispersion of finely divided copper-rich particles.

FIG. 3 illustrates an alloy containing 20% copper, after primaryreduction, and FIG. 4 depicts the same alloy after heat treatment, eachenlarged about 3600 diameters. In these pictures, the prominent insularareas which occupy most of the field of view are plateau-like irongrains surrounded by copper-rich valleys eroded by the acid. There maybe a tendency here for the iron grains to appear to the eye asdepressions, but this apparent steroscopic reversal is an opticalillusion which can be attributed to the lighting. It will be noted thatin the specimen after primary reduction, the iron grains are irregularin shape, whereas after heat treatment they have become rounded orspheroidized.

At high magnification, cracks are detected in the reduced specimen,about 2500 A. in length and 850 A. in Width. These may account at leastin part for the higher shrinkage which occurs upon sintering, and theyare absent in the particles after heat treatment.

The following are the average dimensions observed in the 20% copperalloy after primary reduction at 1125 C., as determined by Zeiss countermeasurements:

Iron grains:

Upon close inspection, the iron grains of FIG. 4 present a much roughertexture than those of FIG. 3, the reason for which is revealed bygreater magnification. FIG. 5 represents a portion of the field of viewof FIG. 4, enlarged about 17,700 diameters. The most prominent featureof the illustration is an elongated valley or copperrich area separatingportions of two adjacent iron grains. The pictured area within thoseiron grains is pitted by erosion of copper-rich particles through theacid treatment, and it is seen that the copper particles within the irongrains fall into two different size groups: primary particles having adiameter of about 01-05 7, and secondary particles having a diameterless than about 0.05 2.

This unexpected and unique structure only appears after heat treatment,and it seems likely that the larger primary particles representagglomeration of the original copper particles in the reduced specimens,resulting from the difference in solubility of copper in iron at thereduction temperature (about 8% at 1125 C.) and at the heattreatingtemperature (about 1.4% at 835 C.) It may be theorized that the primarycopper particles represent the copper in excess of solubility at theheat treating temperature, which agglomerates during such treatmentstep. It may further be theorized that the smaller secondary particlesrepresent that copper which dissolved in the iron to saturation at theheat-treating temperature and subsequently separated during cooling toroom temperature. The fact that these secondary particles are similar insize to the copper particles present within the iron grains afterprimary reduction lends credence to this hypothesis. Nevertheless, itshould be understood that the present invention is not limited by anytheory or hypothesis, however plausible.

The following are the average dimensions observed in the 20% copperalloy after heat treatment at 835 C.

Iron grains: Microns Length 20.09 Width 16.39 Intergranular spacing 1.66

8 Primary copper particles within iron grains:

Microns Length 0.2713 Width 0.2404 Intergranular spacing 1.66 Secondarycopper particles within iron grains:

Length 0.0331 Width 0.0254 Interparticle spacing 0.0287 [ron particlesin copper-rich areas:

Length 0.1238 Width 0.1122 Interparticle spacing 0.4720

The dispersion of more copper Within the iron grains in the alloys ofthe present invention may account for their higher sintered strengthrelative to conventionally infiltrated alloys of equivalent density,whose copper content would appear to be more concentrated between thegrains.

Microscopic examination of the novel alloys of this invention aftercompacting and sintering has also been conducted, and it is found thatthe alloys as sintered closely resemble the unsintered particles. Thiscan be seen by comparing the average iron grain sizes and intergranulardistances in the heat-treated powders and the sintered parts whichresult, e.g. for the 20% copper alloy;

Distance Iron grain between iron Length, [l Width, p grains, n

Heat-treated powder 20. 09 16. 39 1. 66 Sintered part 22. 09 17. 39 1.68 Conventional infiltratioiL 56. 66 27. 91 8. 33

Distance Iron grain between iron Length, ,1 Width, ,1 grains, t

Sintered part from heat treated powder 16. 28 14. 00 3. 41 Conventionalinfiltration 40. 01 22. 66 12. 51

The porosity of sintered iron compacts is ordinarily such that it isnecessary to introduce in excess of 10- 15% copper for adequateinfiltration by conventional technique. Accordingly, for a standard ofcomparison for the new alloys of low copper content, it is necessary toturn to sintered parts made from blended copper and iron powders.Sintered bars containing 7% copper and prepared from a blend of meshcopper and iron powders, when microscopically examined, exhibit largeangular pores and massive copper areas 30 and more in diameter. Thesintered compact prepared from the new particulate alloy containing 7%copper, on the other hand, exhibits a very fine, uniform, close-packedstructure.

The excellent physical properties provided by the new particulatecopper-iron alloys can be even further enhanced by various techniques,providing tensile strengths as high as 150,000 p.s.i. For instance, theincorporation of minor proportions of graphite before molding andsintering afiords increases of from 30,000 to 60,000 p.s.i. in tensilestrength. Graphite levels of about 0.52% are usually adequate.Re-pressing and re-sintering (coining) operations are also beneficialfor increasing density and strength, as are various post treatments,such as quenching, drawing and normalizing, as further illustrated inthe examples which follow.

Provision of the following examples for illustrative purposes is notintended to restrict the invention, the scope of which is defined by theappended claims.

Example l.7% copper alloy (A) Reduction: Grams Iron mill scale 1247.1Dried cement copper 77.0 Hydroxyethyl cellulose 5.3 Water 285.0

The iron mill scale of the above formulation is a byproduct of steelblooming or finishing mills, finer than 325 mesh with about 50% i5%coarser than 20 microns. It has an apparent density of 1.8-2.2 grams percubic centimeter and an analysis as follows:

As FeO 70.50

The cement copper of the above formulation is a byproduct of mine wastewater, finer than 20 microns with about 85% finer than 10 microns. Ithas an apparent density of 0.8-1.5 grams per cubic centimeter and ananalysis as follows:

Percent Cu 1 90.80 8.03 Zn 0.22 Fe 0.47 SiO 0.03 Other metals 0.26Soluble nitrates 0.01 Soluble chlorides 0.08 Soluble sulfates 0.10

A Cu, 2.91; as C1120, 96.72; as CuO, 2.61.

The ingredients are combined and milled into pellets in a mix muller orchaser, which permits intimate admixture with a minimum of grindingaction. The resulting .pellets are charged to a reduction furnace atabout 1120-1135" C. and held at that temperature in hydrogen ordissociated ammonia for 45 minutes. After reduction the pellets areremoved from the furnace and broken up, first in a hammer mill to 4 inchand smaller, and then in a micropulverizer so that all particles arefiner than 80 mesh. The product has an apparent density of 2.3-2.5 gramsper cubic centimeter and an oxygen content of about 1.6% (obtained byreduction in hydrogen at 1050 C. for 30 minutes) or 2.37% (obtained byLeco meth0d melting in vacuum at 3500 F.). The hydrogen weight lossreflects only reducible oxygen content.

Hematite (Fe O or magnetite (Fe 'O -Feo) in sufficient quantity toprovide the same iron content may be substituted for the iron mill scalein the above formulation. In the same way, pure cuprous oxide may besubstituted for the cement copper. j

For the reduction step, carbon monoxide may be substituted for hydrogen,or gases rich in carbon monoxide or hydrogen, such as producer gas, maybe used.

(B) Heat Treatment:

150 grams of the reduced powder is charged to the reduction furnace,maintained at 825-845 C. for one 10 hour, and cooled. The powder isdischarged from the furnace as a loosely sintered mass and reground topowder finer than 80 mesh in the same manner as after the primaryreduction. The annealed powder has an oxygen content of 0.3% (by weightloss in hydrogen) or 1.14%

(Leco method).

Example 2.--1 and 2% copper alloys Grams Iron mill scale 1314.2 'Cupricnitrate trihydrate 37.5 or 76.0 Carboxymethyl cellulose 6.2 Water 300.0

The above formulations are reduced at 1150 C. and heat-treated in thesame manner as is described in Example 1. Hematite (Fe O or magnetite(Fe O -FeO) in sufficient quantity to provide the same iron content maybe substituted for the iron mill scale.

The cupric nitrate may be replaced by equivalent proportions of cupricoxide and nitric acid, or by an equivalent proportion of cupric acetate.

Example 3.-14% copper alloy With 1% nickel Grams Iron mill scale 1153.3Dried cement copper 154.0 Animal protein glue 6.0 Water 270.0 Nickelnitrate (20.3% Ni) 49.5

This formulation is pelletized, reduced at 1110" C. and heat-treated asdescribed in Example 1. Equivalent quantities of hematite (Fe O andnickelous acetate tetrahydrate may be substituted for the iron millscale and nickel nitrate. An equivalent proportion of pure cuprous oxidemay be substituted for the cement copper.

Example 4. 20% copper alloy Grams Iron mill scale 1072 Dried cementcopper 205.2 Cupric nitrate trihydrate 37.1 Lampblack 105.1 Methylcellulose 7.9 Water -153 Grams Iron IIllll scale 1072.8

Dried cement copper 220.5

Molybdic oxide 15.0 Ammonia water (26 B.) 34.0 Carboxymethyl cellulose6.0 Water 275 A similar alloy containing 1% tungsten is prepared in thesame manner, by substituting 12.6 grams of tungstic anhy dride (W0 forthe molybdic oxide in the above formulation. An equivalent cobaltcontent is provided by substitutmg 14.1 grams of cobaltic oxide (C0 0for the molybdic oxide. Hematite (Fe O may also be substituted for theiron mill scale by appropriate adjustment in the quantity added.

Example 5.Particle size elfect scales of varying particle size. Theresulting reduced powders are compacted at 50 tons per square inch,sintered in Example 9.-Heat-treatment effect The procedure of Example 8is repeated, this time confining each heat treatment to a -60-minuteperiod while 14 and sintered as in the previous examples, in both theas-reduced and as-heat-treated forms, with results as follows: I

Tensile Elonga- Sintered Linear strength, tion, density, shrinkage,

p.s.i. percent g./cc. percent Hardness 1% cobalt:

Reduced 31,800 1. 9 5. 97 1. 43 B 29. 1 Heat-treated 55, 200 4.0 6. 790. 72 B 59. 7 1% nickel:

Reduced 32, 400 1.9 5. 94 1. 54 B 33. Heat-treated 65, 100 2.3 6.77 0.90B 70.9 1% molybdenum Reduced 35, 300 1.8 5. 90 1.73 B 28. 1Heat-treated- 65, 500 1. 9 6. 90 0. 69 B 74. 5

more closely exploring the temperature range between 810 and 850 C.,with temperatures controlled to i2 C. Six test specimens are molded fromeach batch, with averg./cc. and the Sintered densities from 6.52 to 6.84g./cc., for this series of tests.

Example 10.-Heat-treatment effect The procedure of Examples 8 and 9 isrepeated, this time subjecting a 7% copper alloy powder to heattreatment at 835 C. for periods of 30, 45 and 60 minutes, with thefollowing results:

Heat treatment for (minutes) 30 45 60 Compact: Green density, gJcc. 5.91 6. 40 6. 65 Sintered Compact:

Linear shrinkage, percen 1. 21 0. 97 0. 79 Tensile strength, p.s.i 56,700 58, 100 63, 300

Example 13.-Use of elemental copper The procedure of Example 1 isrepeated, this time substituting for the cement copper an equivalentproportion (70 grams) of atomized copper powder finer than 100 mesh. Thereduction is conducted at 1000 C. for minutes, with heat treatment at835 C. for one hour. After compacting and sintering as before,thereduced and heat-treated powders provide the following properties:

- Reduced Heat-treated Tensile strength, psi. 52, 400 65, 800Elongation, percent" 0. 8 1. 0 Sintered density, g./cc 6. 39 6. 70Lineanshrinkage, perce 0.85 0.09 Hardness B 61. 3 B 68. 4

Example 14.-Other copper sources The procedure of Example 1 isrepeated,substituting for the cement copper equivalent quantities inproportion to their copper content of various other copper sources.After reduction at 1125 C. for 45 minutes and heat treatment at 825-845C. for one hour, the powders are pressed and sintered as before to yieldthe following properties:

Example 11.-Reduction temperature and 45 Si d T ntere ensile heattreatment effects Copper source density,g./cc. strength, p.s.i. Samplesof each of the reduced powders prepared in Cum; Oxide (833% (mm M150,100 Example 7 are heat-treated for one hour at 835 C. The gop er m nlscaleN(88.1 6%576 gm 2. g $53 emen opper o. heat-treated powders arethen compacted and smtered as Cement Copper 2 (93.04% 688 68,000 before,and subjected to physical testing, with results was Reduced copperpowder 09. 52% Cu 6.75 69,200 follows: 2

Reduction temperature Batch Batch Heat treated powder:

Apparent density, gJec 2. 44 2. 12 2. 10 2. 69 2. 58 2. 57 Flow rate,see/50 g 33.3 38.6 None 25.3 25.7 25.0 325 mesh, percent- 40. 5 53. 960. 0 34. 1 40. 2 45. 0 Hz wt. loss, percent 1 0.51 0. 52 0. 67 0. 300.22 0.20 Compact: green density, gJec 6. 48 6. 37 6.30 .6. 6.73 6.66Sintered compact:

Sintered density, g./cc 6. 68 6. 55 6. 52 6. 83 6. 80 6. 76 Tensilestrength, p.s.i 53, 500 49, 000 47, 500 63, 300 61,100 62, 600Elongation, percent 1. 9 2. 0 1.8 3. 1 3. 2 2. 9 Linear shrinkage,percent 1. 49 1.31 1. 53 0. 79 0.77 0.64 Hardness B 60.9 B 59.4 B 63.0 B63.3 B 58.9 B 60.4

1 1,100 C. for 30 minutes.

Example 12.-Eifect of other metals In accordance with the procedures ofExamples 3 and 4, 7% copper alloy powders are prepared, each containing1% cobalt, nickel or molybdenum. These are compacted with 0.75% stearicacid, compacted at various pressures,

Example 15.Effect of compacting pressure A 7% copper alloy powder,prepared by reduction and heat treatment as described in Example 1, iscombined and each compact is sintered at 1120 C. for 45 minutes inhydrogen. The physical properties, as a function of compacting pressure,are found to be as follows:

Compacting pressure (t.s.i.)

Example 16.--Graphite effect with varying compacting pressures Example15 is repeated, this time incorporating 1% graphite in each heat-treatedpowder prior to compacting and sintering, with results as follows:

Compacting pressure (t.s.i.)

Compact: Green density, g./cc- 5. 96 6. 33 6. 68 6. 78 Sintered compact:

Sintered density, g./cc 6 0 Tensile strength, p.s.i. Elongation, percentLinear shrinkage, percent- Hardness 7 0.43 6.80 0.01 72,700 91,500100,100 137,000 1.9 2.0 2.0 0.0 0. 86 0. s4 0. s1 0. 80 B 72.3 B 83.2 B86.9 B 100.2

Example 17Coining effect The procedure of Examples 15 and 1 6 arerepeated, this time subjecting the final sintered piece to re-pressingand re-sintering under the same conditions used in the firstpressing-sintering cycle. The properties achieved are summarized below:

Compacting pressure (t.s.i.)

Compact: Green density, g./cc 6. 6.63 6. 76 6. 74 Sintered compact:

Sintered density, g.lce 6. 83 6. 79 6. 92 6.90 Re-pressed density, g./cc6.86 6. 81 7. 13 7.05 Re-sintered density, g./cc 6. 93 6. 85 7. 20 7. 11Final tensile strength, p.s.l 77, 200 111, 300 82, 900 123, 600 Finalelongation, percent. 3. 0 2. 0 5. l 3. 0 Final hardness B 94. 2 B 85. 3B 99. 7 Linear shrinkage, percent:

After 1st sintering 0. 79 0. 91 0. 75 0. 78 After 2nd compaction 0. 080. 01 0. 06 0. 01 After 2nd sintering 0.07 0. 01 0. 05 0. 01

1 1% graphite additive.

Example 18.-Graphite effect with varying copper content Copper content(percent) Compact: Green density, g./cc 6. 63 6. 68 6. 86 6. 97 sinteredcompact:

Sintered density, g./ce 6. 76 6. 80 7. 2O 7. 46

Tensile strength, p.s.i 103, 700 109, 100 112, 000 112, 900

Elongation, percent 2.1 2.0 2. 0 1. 9

Linear shrinkage, percent 0. 77 0.81 1. 46 1. 96 Hardness B 88.3 B 86.9B 97.4 B 101.5

Example 19.Post-sintering treatments Sintered compacts prepared as inExample 18 are subjected to various additional treatments to furtherenhance physical properties, with results as follows:

Copper content (percent) Without graphite:

Aged density, g./cc 6. 7 6. 78 7. 33 7. 59 Aged tensile strength, p.s.i73, 300 96, S00 85, 600 77,400 Elongation. percent 2. 0 1. 9 2. 1 2. 0Linear shrinkage as aged,

0.48 1. 65 2. 47 B 84.4 B 92.0 B 95.9 With 1% graphite:

Aged density, g./ce 6. 72 6. 74 7. 26 7. 51 Aged tensile strength, p.s.i118, 100 133, 300 147, 000 137, 200 Elongation, percent 1. 1. 9 1. 9 2.0

Linear shrinkage as aged,

percent Hardness.

1 Quenched in water from sintering and aged at 485 C. in hydrogen for 30minutes.

2 Normalized in nitrogen at 1,000 C. for 60 minutes after sintering,then furnace-cooled to 370 0., held at 815 C. in hydrogen for IO-minutesoak, quenched from this temperature in water, and finally aged at 2600. one hour in air.

0. 83 0. 63 1. 58 1. 89 B 85.4 B 34.4 B 110.8 B 109.4

Example 20.Eifect of copper content in reduced powders A series offerrous alloy powders of varying copper content is prepared by thereduction procedure of Example 1A, with appropriate adjustment in thecement copper charged. The reduced powders are blended with 0.75%stearic acid lubricant, compacted at 50 t.s.i. and sintered at 1120 C.for 45 minutes in hydrogen. The physical properties are summarized inthe table below:

Percent Percent Sintered Tensile, Linear density, X10- Elongashrink-Copper 0 1 g./ec. p.s.i tion age Hardness 5. 90 37. 8 1. 9 1. 82 B 27. 25. 90 38. 0 1. 9 1. 84 B 29. 7 5. 92 38. 5 1. 1 1. 81 B 35. 2 5. 96 39.6 1. 0 1. 81 B 34. 0 5. 98 39. 7 1. 0 1. B 35. 5 6. 08 40. 4 1. 9 2. 20B 42. 2 6. 29 45. 9 1. 8 2. 35 B 49. 3 6. 37 48. 9 2. 0 2. 64 B 51. 6 6.54 51. 6 2. 1 3. 17 B 55. 6 6. 75 56. 6 2.0 3. 61 B 68. 2 6. 87 60. 5 3.0 3. 68 B 69. 6 6. 81 79. 7 3. 9 8. 13 B 90. 9 6. 88 58. 2 3. 8 8. 48 B86. 4 7.27 42.0 4. O 8. 44 B 53. 8

- As indicated by percent weight loss in hydrogen at 1,100 C. for 30minutes.

2 Reduced at 1,050 O. for 30 minutes; sintered at 1,120 O. for 10minutes.

3 Reduced at 950 C. for 30 minutes; sintered at 1,120 C. for 10 minutes.4 Reduced at 950 C. for 30 minutes; sintered at 1,095 C. for 10 minutes.

Example 21.Eifect of copper content in heattreated powders Reducedpowders prepared as described in Example 20 are heat-treated at 835 C.for 60 minutes in hydrogen, before compacting at 50 t.s.i. and sinteringat 1120 C. for

45 minutes in hydrogen. The effect of the heat treatment on physicalproperties is summarized in the table below:

Percent Percent Sintered Tensile Linear density, Percent 10-Elongashrinkg./cc. Porosity p.s.1. tion age Hardness 6.80 13. 8 49.0 4.9 0. 77 B 42.2 6. 82 13. 8 51. 6 4. 8 0. 80 B 50.0 6. 83 14.0 58. 3 3. 90.75 B 53.9 6. 83 14. 1 63. 3 3. 1 0. 79 B 63.3 6.89 13.4 68.9 4.0 0.93B 66.1 6. 89 13. 6 82. 8 3. 9 1. 14 B 77.2 7. 02 12. 3 83. 7 4.1 1. 32 B80.0 7. 12 11. 2 84. 8 4. 1. 55 B 80.9 7. 23 10. 1 85. 9 4. 0 1. 97 B83.1 7. 38 8. 4 86. 7 3. 9 2. 32 B 84.8 7. 46 7. 8 87. 4 4. 1 2. 58 B88.1 7. 48 8.8 87.3 3.0 1. 39 B 89.3 7. 55 9. 3 78.9 3.1 2.03 B 79.7 7.75 8. 1 66. 4 3. 9 2.18 B 76.5

1 As indicated by percent weight loss in hydrogen at 1,100 C. for 30minutes. 2 Reduced at 1,050 C. for 30 minutes; sintered at 1,120 C. for10 minutes. 3 Reduced at 950 C. for 30 minutes; sintered at 1,120 C. for10 minutes. 4 Reduced at 950 C. for 30 minutes; sintered at 1,095 O. for10 minutes.

Example 22.Copper-iron powder blends Example 24.Reduction temperatureFor purposes of comparison, a series of copper alloys Grams is preparedby prior art procedures, by blending appropri- Iron mill scale 2376 ateproportions of 100 mesh reduced elemental copper and Copper fine dust288,7 iron powders for minutes, compacting at 50 t.s.i. and Coke (Cabot)303.8 sintering at 1120 C. for 45 minutes in hydrogen. The Sugar(Sucrose) 38.1 properties obtained are summarized below: Water 330.7

Percent Sintered Linear density, Percent Tensile, Elongashrink- Percentcopper g./cc. porosity l0- p.s.i. tion age 1 Hardness 6.28 20.4 35.6 4.90.01 B 25.5 6. 30 20. 7 40.0 2. 9 0. 92 B 21.4 6.37 20.7 42.1 1.6 1. 88B 39.3 6. 20.2 45.2 2.3 2.04 B 20.2 6.49 19.8 44.3 2.3 2.24 B 19.7 7.0216.6 26.6 4.5 0.99 B 3.2

1 All samples expand on sintering. 2 Sintered at 1,000 C. for 30minutes.

Heat treatment of the powder blends by the procedure of Example 21 priorto compacting has no significant effect on the results.

Example 23.Impact strength The impact strengths of the novel alloys ofExample 21 are compared with the values for conventional alloys preparedfrom blended copper iron powders as in Example 22, and with ironcompacts infiltrated with copper in the conventional manner, withresults as follows:

Impact strength, it./lbs.

Percent copper Process Oharpy Izod Tension 7 Exafinple 21 7 +1 raphite)o .5 Bleraded powders. g g 3 7 (+1 raphitc o 1L??? Example 21 4. 6 15Conventional 3. 2

infiltration. 25 d0 5. 0

. Example 21- 5. 3

The above ingredients are combined, milled into pellets, and reduced in600 gram batches at 2000 F., 1850 F. and 1800" F. The gases evolved,containing carbon monoxide and carbon dioxide, are vented and burned.Thus, continuing combustion of vented gas provides an indication thatthe reduction is continuing. The reduction times required to approachburn out (completion of recation) are:

1 hr. 48 min 2000 2 hrs. 35 min. 1850 7 hrs. 20 min. 1800 The reducedcakes (12% copper) are crushed, ground and heat-treated at 1830 F. forone hour and then at 1535 F. for 30 minutes in dissociated ammonia. Theannealed cakes are then crushed, ground and screened to mesh.

The comparative powder properties are:

l Pressing at 40 t.s.i. and sintering at 2,050 F. 35 minutes.

What is claimed is:

1. A process for preparing a particulate alloy comprising ironinfiltrated with from about 1 to 50% by weight of copper, said processcomprising the steps of mixing a reducible compound of iron with anappropriate proportion of a copper compound selected from the groupconsisting of elemental copper and reducible compounds of copper,heating said mixture under reducing conditions at a temperature betweenabout 1010 (1850 F.) and 1150 C. (2100 F.), continuing said heatinguntil said reducible compounds are substantially completely reduced tothe metallic state having an iron-rich phase, subjecting saidparticulate alloy to heat treatment by maintaining said alloy for atleast about 5 minutes at a temperature between the oz-'y transitiontemperature of the iron-rich phase of said alloy and a temperature ofabout 150 C. below said transition temperature and thereafter coolingthe alloy.

2. The process of claim 1 wherein the temperature during said reductionstep is below the melting point of copper.

3. The process of claim 1 wherein the temperature during said reductionstep is between about 1038 (1900 F.) and 1066 C. (1952 F.).

4. The process of claim 1 wherein said reducible mixture ischaracterized by a particle size finer than about 250 microns.

5. The process of claim 1 wherein said iron compound has a particle sizefiner than about 50 microns and said copper compound has a particle sizefiner than about 20 microns.

6. The process of claim 1 wherein said iron compound is an oxide ofiron.

7. The process of claim 6 wherein said iron compound comprises hematite.

8. The process of claim 6 wherein said iron compound comprisesmagnetite.

9. The process of claim 6 wherein said iron compound is a reducible millscale.

10. The process of claim 1 wherein said copper compound is an oxide ofcopper.

11. The process of claim 10 wherein said copper compound is cuprousoxide.

12. The process of claim 10 wherein said copper compound is copper fluedust.

13. The process of claim 1 wherein said copper compound is water-solubleand is introduced in the form of a water solution.

14. The process of claim 13 wherein said copper compound is cupricnitrate.

15. The process of claim 1 wherein said copper compound is elementalcopper.

16. The process of claim 1 wherein said reducible mixture includes aminor proportion of a substance selected from the group consisting ofnickel, cobalt, molybdenum, tungsten, and reducible compounds of saidelements.

17. The process of claim 1 wherein said reducible mixture is blendedwith an aqueous dispersion of an organic adhesive prior to saidreduction step.

18. The process of claim 1 wherein said reducing conditions are providedby incorporating finely divided carbon in said reducible mixture.

19. The process of claim 1 wherein said heating is conducted in areducing atmosphere.

20. The process of claim 1 wherein said heat-treating temperature isless than C. below said transition temperature.

21. The process of claim 1 wherein said heat-treatment is conducted at atemperature between about 825 and 845 C.

References Cited UNITED STATES PATENTS 2,200,369 5/ 1940 Klinker 0.52,754,193 7/1956 Graham et a1 750.5 2,754,194 7/ 1956 Graham et al.750.5 2,754,195 7/1956 Graham et al. 750.5 2,853,767 9/1958 Burkhammer750.5

L. DEWAYNE RUTLEDGE, Primary Examinet W. W. STALLARD, Assistant ExaminerU.S. Cl. X.R.

